conunting atoms in simple molecules with coefficients answer key

3 min read 23-01-2025

conunting atoms in simple molecules with coefficients answer key

Meta Description: Learn how to count atoms in simple molecules using coefficients. This comprehensive guide provides a step-by-step approach, examples, and an answer key to practice problems. Master the basics of stoichiometry with ease! (158 characters)

Understanding Chemical Formulas and Coefficients

Counting atoms in molecules is a fundamental skill in chemistry. It's crucial for understanding chemical reactions and stoichiometry. Chemical formulas show the types and numbers of atoms in a molecule. For example, H₂O (water) indicates two hydrogen atoms and one oxygen atom.

Coefficients are numbers placed in front of chemical formulas. They tell us how many molecules of a particular substance are involved in a reaction. For example, in the reaction 2H₂ + O₂ → 2H₂O, the coefficient "2" in front of H₂ means there are two molecules of hydrogen.

Identifying Atoms and Coefficients

Before we start counting atoms, it's essential to differentiate between subscripts (small numbers within the chemical formula) and coefficients (numbers before the chemical formula). Subscripts indicate the number of atoms of a specific element within a single molecule, while coefficients indicate the number of molecules.

Example: In the formula 3H₂O, "3" is the coefficient (3 water molecules), "2" is the subscript (2 hydrogen atoms per water molecule), and there's an implied "1" as the subscript for oxygen (1 oxygen atom per water molecule).

How to Count Atoms in Molecules with Coefficients

Here’s a step-by-step process:

Identify the coefficient: Find the number preceding the chemical formula. If there's no number, the coefficient is 1.
Identify the subscripts: Locate the small numbers following each element symbol in the formula. If an element lacks a subscript, it implies a subscript of 1.
Multiply the coefficient by each subscript: For each element, multiply its subscript by the coefficient. This gives you the total number of atoms of that element in the given number of molecules.
Sum up for each element: This will give you the total number of atoms for each element in the entire expression.

Worked Examples

Let's practice with some examples:

Example 1: 2CO₂

Coefficient: 2
Carbon (C): Subscript 1, total atoms: 2 × 1 = 2
Oxygen (O): Subscript 2, total atoms: 2 × 2 = 4
Total: 2 carbon atoms and 4 oxygen atoms.

Example 2: 4NH₃

Coefficient: 4
Nitrogen (N): Subscript 1, total atoms: 4 × 1 = 4
Hydrogen (H): Subscript 3, total atoms: 4 × 3 = 12
Total: 4 nitrogen atoms and 12 hydrogen atoms.

Example 3: 3H₂SO₄

Coefficient: 3
Hydrogen (H): Subscript 2, total atoms: 3 × 2 = 6
Sulfur (S): Subscript 1, total atoms: 3 × 1 = 3
Oxygen (O): Subscript 4, total atoms: 3 × 4 = 12
Total: 6 hydrogen atoms, 3 sulfur atoms, and 12 oxygen atoms.

Practice Problems: Counting Atoms

Instructions: Calculate the total number of atoms for each element in the following molecules.

5NaCl
2H₂O₂
3Mg(OH)₂
6CO(NH₂)₂
2(NH₄)₂SO₄

Answer Key

5NaCl: 5 Na atoms, 5 Cl atoms
2H₂O₂: 4 H atoms, 4 O atoms
3Mg(OH)₂: 3 Mg atoms, 6 O atoms, 6 H atoms
6CO(NH₂)₂: 6 C atoms, 6 O atoms, 12 N atoms, 12 H atoms
2(NH₄)₂SO₄: 4 N atoms, 16 H atoms, 2 S atoms, 8 O atoms

Conclusion

Counting atoms in molecules using coefficients is a fundamental concept in chemistry. By following the steps outlined above and practicing with the provided examples and problems, you can confidently master this skill. Remember the importance of distinguishing between subscripts and coefficients for accurate atom counting. This skill forms the basis for understanding chemical reactions and stoichiometry, essential topics in further chemical studies.